Tachyon MCP

Tachyon MCP is an open-source Java 21+ server runtime for the Model Context Protocol, built on Netty and licensed under Apache 2.0. It is developed by IT Staff OÜ and Konstantin Pavlov, and passes the official MCP conformance suites for both the 2025-11-25 and 2026-07-28 protocol versions. Developers write synchronous Java handlers or coroutine-first Kotlin handlers, and Tachyon handles all transport and protocol details.

What It Is

Tachyon MCP is a server-side framework that lets Java and Kotlin developers build Model Context Protocol servers without managing reactive pipelines, manual thread pools, or wire-format details. It sits between the application logic (tools, resources, prompts) and the MCP transport layer, running blocking handlers on virtual threads and keeping them off the Netty event loop. The project requires no application framework, though it also ships a Spring Boot starter for teams that want one.

Protocol Coverage and MCP Surface

Tachyon implements a broad MCP surface area across both supported protocol versions:

• Tools, resources and templates, prompts, completions — the core MCP primitives
• Logging, sampling, elicitation, cancellation, subscriptions, pagination, and progress notifications — full lifecycle support
• Tasks — full tasks/* lifecycle with state validation, status notifications, retention, and a TasksExtension implementing SEP-1686
• Agent Skills — SkillsExtension implementing the SEP-2640 draft: filesystem and classpath registries, skill:// resources, skills/list, skills/get, and directory reads
• Extensions — SEP-2133 negotiation, custom JSON-RPC methods, capability advertisement, and extension-gated features

Runtime Architecture

The transport layer is Netty, which owns the socket and connection lifecycle. Tachyon auto-detects the best native transport available (io_uring → epoll → kqueue → NIO). Key runtime properties include:

• Stateless by default, with opt-in resumable sessions, Last-Event-ID replay, and TTL cleanup
• DNS-rebinding guard on Host/Origin headers, accepting localhost only by default
• Graceful shutdown that allows in-flight handlers to finish
• Netty backpressure and CORS support
• Built-in OpenTelemetry integration via tachyon-opentelemetry, following MCP semantic conventions, with an opt-in payload capture policy

Annotation and Framework Adapters

Tachyon supports a declarative annotation model (@McpTool, @McpParam) for defining tools on plain Java or Kotlin classes. It also ships optional adapters that bridge existing annotated services from mcp-java, LangChain4j, and Spring AI into Tachyon's standard registries, so teams can reuse existing service code without rewriting handlers. A Spring Boot starter is available for teams that prefer convention-over-configuration setup.

Developer Experience and Testing

The project ships a testkit (tachyon-testkit) for end-to-end testing of running servers through an MCP client, with support for dynamic-port servers and fluent JSON-RPC assertions. The repository also includes a coding-agent skill that teaches agents how to build Tachyon servers, installable via npx skills add tachyonmcp/tachyon --skill tachyon-mcp. Documentation covers Java quickstart (Maven/Gradle), Kotlin DSL, Spring Boot integration, configuration, deployment, observability, and a migration guide from the Kotlin SDK.

Update: v1.0.0-beta.31

The latest release as of late September 2026 is v1.0.0-beta.31, published on 2026-09-25. The project was created in June 2026 and has seen rapid iteration, with the repository last pushed on 2026-09-26. The current beta status reflects active development toward a stable 1.0 release, with conformance testing against both the 2025-11-25 and 2026-07-28 MCP specifications already passing.